Category Archives: Radio history

1957 Hi-Fi Phono Oscillator

1957RadioTVExpCover

Maybe your MP3 player sounds a bit better than this gentleman’s hi-fi turntable from 60 years ago, but I bet you can’t build yours from scratch, like this guy did.  This one, shown on the cover of the 1957 edition of Radio-TV Experimenter, is entirely homemade, and despite the homemade appearance, probably did sound as good or better than anything on the market at the time, and would probably have sounded good even by today’s standards.

It was actually a phono oscillator, and transmitted the signal through an FM transmitter.  Since the audio quality of the FM signal was better than the recording technology of the day, the fidelity was limited only by the quality of the record.

Sound quality was paramount in every detail.  As is plainly visible, the tone arm is indeed made out of wood.  In particular, the wood is basswood, chosen because it had less mechanical resonance than other woods.  Metal would have been inferior, because of the capacitive effect with the leads running through it.

The pickup was homemade, not as a cost-saving measure, but because the design shown here was superior to the ceramic cartridges then commercially available.  It used a capacitive pickup.  The only commercial component was the sapphire-tiped needle, which was pushed into a rubber plug.  A copper plate was carefully positioned next to the needle to complete the capacitive pickup.

The tone arm was cut with a jigsaw, and the article contained precise instructions for balancing it.

The electronics, probably the easiest part to construct, consisted of a small FM transmitter employing a single 6C4 tube.  The example shown here was to be used for 45 RPM records, but the article noted that by adjusting the size and using an appropriate needle, it could be built for 33 or 78 RPM records.



Politically Incorrect Marketing of Radio Parts, 1947

1947MayRadioServDealerSeventy years ago this month, Olson Radio Warehouse had a promotional idea that would probably be regarded as somewhat on the politically incorrect side today. To encourage radio servicemen to order parts and supplies, they instituted the Gift of the Month Club. When the serviceman placed an order, Olson would toss in a free gift. And they kicked the program off by giving away free cigarettes! That’s right: When the serviceman ordered tubes or resistors, Olson would throw in a pack of Camels, Chesterfields, or Luckies!

This piece of trade news appeared in the May 1947 issue of Radio Service Dealer. It reveals that, as of press time, Olson had handed out a quarter million free smokes.



1942 Handheld Radiotelephone

1942MayRadioCraft1

1942MayRadioCraft2Seventy-five years ago this month, the May 1942 issue of Radio Craft featured on its cover this handheld radio telephone weighing only four pounds, which the magazine noted was not much larger than the handset of a “French” telephone. The set was the product of the Weltronic Corporation, which was the assignee of the patent, U.S. Patent 2276933, with a pre-Pearl Harbor application date of October 1, 1941, and an issue date of March 17, 1942.

1942MayRadioCraftDiagramThe magazine noted that the set had a range of about a mile, and could operate on any frequency between 112-300 MHz. The diagram below reveals that the set appears to be one tube functioning as an oscillator and superregenerative detector, with the other tube serving as AF amplifier to drive the headphone on receiver, and as modulator on transmit.

Commercially available batteries were said to allow continuous operation for eight hours, or about a week to a month in normal service. The article noted that the set was being made available to governmental agencies.

The cover photo shows the unit in use by a guard around a defense plant.

The article puts quotation marks around the word “transceiver,” since such a combined unit would have been unfamiliar to many readers.

1942MayRadioCraftSchematic

 



1977 Wrist Calculator

1977MayEEForty years ago, electronic calculators had been on the market for a few years, and they were starting to get smaller and cheaper. Those who wanted the smallest calculator might have given some consideration to this kit advertised in the May-June 1977 issue of Elementary Electronics.

Offered by Sinclair (the same people who put out one of the first inexpensive home computers), the wrist calculator sold in kit form for only $19.95. The ad noted that a pocket calculator was good, but goes only where your pocket goes. “Take your jacket off, and you’re lost.”

The wrist calculator, on the other hand, was always with you whenever you had calculating needs.

The calculator featured an eight digit display, and to squeeze in the keyboard, it used ten keys “do the work of 27.” The digits 1-0 were marked on the keys. But on the side of the case was a three position switch. In the center position, the keys entered the numbers. But when set to the left and right, the keys became function keys. In addition to the normal four functions, the calculator boasted percentage, square root, reciprocal, and square. It also had a five-function memory.

A set of readily available hearing aid batteries were said to give weeks of service. All parts were included, and assembly required only a fine-point soldering iron.



Coronation of King George VI, 1937

The Coronation of King George VI and Queen Elizabeth (the mother and father of the current Monarch) took place on this date 80 years ago today, on May 12, 1937.

King George V had died on January 20, 1936, at which time Edward VIII assumed the throne. Shortly thereafter, he caused a constitutional crisis after announcing his plans to marry American divorcee Wallis Simpson. The crisis was resolved by his abdication on December 11, 1936, at which time George VI assumed the throne.

Edward’s coronation was originally scheduled for May 12, 1937, and the event went on as scheduled, with George rather than Edward being crowned.

1937May15RadioGuideThe event was broadcast live by radio in America. Radio Guide for the week ending May 15, 1937 predicted that the event would be “without doubt, radio’s biggest show–the ‘crowning event’ in the twenty-odd years of radio broadcasting’s existence.” The magazine reported that there would be a battery of microphones in place to bring the scene to listeners all over the world.” NBC and CBS planned six hours of continuous coverage.

 



1937 Radio Facsimile

1937MayAllWaveRadio1

Eighty years ago this month, the May 1937 issue of All Wave Radio magazine carried a description by J.F. Gordon, W7CNP, of his method of sending facsimile by radio. The received image is shown above. While the system was quite simple in theory, it does appear to be quite labor intensive.

1937MayAllWaveRadio2The received image, shown above, is reproduced on photographic film. The original transmitted image, drawn in pencil, is shown at the left. Since the entire image is drawn in pencil, it is conductive, and can be scanned by a conductive stylus. There needs to be continuity between all points on the image, and for this reason, the letters are all linked by a pencil line. Before transmission, these lines are covered up with coil dope or another insulating substance.

The image is then scanned on a normal phonograph turntable, powered by a synchronous motor to keep the speed at both ends of the circuit exactly the same. The image is scanned by a stylus riding on a threaded rod geared to the turntable motor.

An audio signal is sent through the circuit from the pencil lead to the stylus, and this signal is used to modulate the transmitter.

1937MayAllWaveRadioTX

At the receiving side, an identical turntable is employed. For receiving, the stylus is replaced by a neon lamp. A piece of photographic film is placed on the turntable, which of course needs to be in a darkened enclosure. A second neon lamp is placed outside the box to make sure the system is receiving properly.

1937MayAllWaveRadioRX

The neon lamp is driven by the receiver audio. Assuming everything is working properly, when the film is developed, it sould reveal a negative image of the original pencil disk.



Training Wireless Operators, 1917

1917MayPMA hundred years ago this month, the May 1917 issue of Popular Mechanics showed this image of woman students at Hunter College, New York.  The women were looking forward to the possibility of wartime labor shortages that would allow them to serve the government as wireless operators.



Marine Direction Finding, 1957

1957MayPE

The mariner shown here 60 years ago on the cover of the May 1957 issue of Popular Electronics is demonstrating two methods of radio navigation described in the magazine, using a National NC-66 receiver and its optional external loop antenna.

Using the receiver alone, she is using the method that required no special direction finding antenna, and that provided accurate results even in a small bouncing boat.

That method used the “A-N” longwave radio ranges which were still operating between 200-400 kHz. While these aeronautical radio ranges were most often used by pilots, there was no reason why they couldn’t be used by boaters, as long as the craft had a longwave receiver aboard.

As we described in an earlier post, each of these beacons transmitted two signals in a four-leaf clover pattern. In two quadrants, the Morse letter A (dot-dash) could be heard. In the other two quadrants, the letter N (dash-dot) could be heard. At the intersections of the two signals (“on the beam” normally followed by pilots), the signals would merge and be continuous.

1957MayPE2For example, a boater shown at the position marked 1 near the bottom of this map would first tune to 227 kHz to beacon HEM at Mitchell Field, Long Island. She would hear the A. Then, she would tune to 248 to listen to the beacon IDL at Idlewild and hear the N. Finally, she could tune in EWR Newark on 341 kHz, where N would be heard.

By consulting the chart and using the process of elimination, this would narrow her location down to the relatively small quadrangle off the New Jersey coast.

The magazine also described the next logical step in navigation skill as use of the optional loop antenna and null meter shown at the top of the picture.  As we’ve described previously, such an antenna would allow an exact bearing to any station, using either a marine beacon or standard AM broadcast station.



1937 Electronic TV Receiver

1937MayRadioNews

Eighty years ago this month, the May 1937 issue of Radio News carried an ambitious construction project, this television receiver. TV receivers had been popular projects in earlier radio magazines, but the earlier ones were all mechanical televisions, employing a spinning Nipkow disk.

This set was all electronic, employing a cathode ray tube.  The construction article did not have an individual byline.  Instead, it was attributed only to “the Don Lee Television Staff,” referring to the Los Angeles broadcaster and licensee of W6XAO.

W6XAO image taken off the air.

W6XAO image taken off the air.

The plans for this set were also included in other magazines, and the broadcaster also made it available in kit form.

While the receiver was all electronic, it appears that the camera was still a mechanical device.  A spinning disk was used to produce a flying spot to convert previously filmed footage to a video signal.  Shortly thereafter, the station appears to have adopted an electronic camera.

The set, including both RF and video sections, contained a total of 14 tubes in addition to the CRT.  It did not contain an audio section.  Presumably, accompanying audio was received on a separate radio receiver.



1942 One Tube Emergency Broadcast Receiver

1942MayPMSeventy-five years ago this month, the May 1942 issue of Popular Mechanics carried the plans for the “Veep” one-tube AC-DC broadcast receiver. The set was built on a simple galvanized chassis, and mounted in a cigar box, the “Veep” name coming from the brand of cigars.

The sew was designed to be rugged and compact, and the part count was kept to an absolute minimum to keep costs down. The set ran off standard household current, eliminating the worry of batteries running down. It was designed for instant emergency use. The set could be kept in a pocket, and in case of need for the latest news, air-raid warnings, or other programs, it ccould be put into action at the plant, office, or home at odd times.

The set used a single 117L7-GT serving as rectifier and detector. Since the set ran right off the line cord, the article warned not to use an external ground connection.

1942MayPM2The set would pull in local stations with a 3-4 foot antenna. For greater range, the antenna could be connected to an ungrounded metal object such as a hand rail or bed springs. While the set was designed for headphone operation, it could drive a speaker for strong local stations.1942MayPMSchematic